1. Field of the Invention
The present invention relates to a method for manufacturing a display device having a stacked-layer structure of thin films, and specifically relates to a processing step of forming a hole in a thin film in a process of manufacturing a display device.
2. Description of the Related Art
Thin film transistors (hereinafter also referred to as TFTs) and an electronic circuit using a thin film transistor are manufactured by stacking of thin films such as semiconductor films, insulating films, or conductive films over a substrate and forming a predetermined pattern as appropriate by a photolithography technique. A photolithography technique is a technique for transferring a pattern of a circuit or the like, which is formed from a light-blocking material on a surface of a transparent planar plate, which is called a photomask, onto a target substrate by utilization of light, and it has been generally used in manufacturing processes for a semiconductor integrated circuit and the like.
A conventional manufacturing process using a photolithography technique requires multiple steps such as exposure, development, baking, and removing even just for processing a mask pattern which is formed with the use of a photosensitive organic resin material that is referred to as a photoresist. Therefore, as the number of the photolithography steps increases, the manufacturing cost inevitably increases. In order to solve this problem, attempts have been made to manufacture TFTs using a smaller number of photolithography steps (for example, see Patent Document 1: Japanese Published Patent Application No. 2000-133636). In Patent Document 1, after a resist mask formed by photolithography steps is used once, it is swelled so that its volume expands and then used again as a resist mask having a different shape.